Many modern aircraft, as well as other vehicles and industrial processes, employ gas turbine engines for generating energy and propulsion. Such engines include a fan, compressor, combustor and turbine provided in serial fashion, forming an engine core and arranged along a central longitudinal axis. Air enters the gas turbine engine through the fan and is pressurized in the compressor. This pressurized air is mixed with fuel in the combustor. The fuel-air mixture is then ignited, generating hot combustion gases that flow downstream to the turbine. The turbine is driven by the exhaust gases and mechanically powers the compressor and fan via one or more central rotating shafts. Energy from the combustion gases not used by the turbine is discharged through an exhaust nozzle, producing thrust to power the aircraft.
Turbofan gas turbine engines contain an engine core and fan surrounded by a fan case, forming part of a nacelle. The nacelle is a housing that contains the engine. The fan is positioned forward of the engine core and within the fan case. The engine core is surrounded by an engine core cowl and the area between the nacelle and the engine core cowl is functionally defined as a fan duct. The fan duct is substantially annular in shape to accommodate the airflow from the fan and around the engine core cowl. The airflow through the fan duct, known as bypass air, travels the length of the fan duct and exits at the aft end of the fan duct at an exhaust nozzle.
In addition to thrust generated by combustion gasses, the fan of gas turbine engines also produces thrust by accelerating and discharging ambient air through the exhaust nozzle. Various parts of the gas turbine engine generate heat while operating, including the compressor, combustor, turbine, central rotating shaft and fan. To maintain proper operational temperatures, excess heat is often removed from the engine via oil coolant loops, including air/oil or fuel/oil heat exchangers, and dumped into the bypass airflow for removal from the system.
Gas turbine engines require a supply of lubricant, such as oil, to mechanical components such as, but not limited to, bearings, seals, and the like. The oil can be used as a lubricant, a coolant or both. Typical oil systems supply the oil to a manifold, which then directs the oil to various engine components. The lubricant may be filtered to remove unwanted debris, and may also be de-aerated to remove any air absorbed by the oil while lubricating and cooling the components. An oil cooler may remove heat gained from the lubricated components.
In prior art oil systems, the quantity of oil pumped to the components is typically based on speed or load conditions. However, either approach may result in an oversupply of oil in low load conditions, such as during cruise or taxiing, for example. This reduces the efficiency of the engine in that the excess oil is pumped through the engine. Additionally, the lubricant then needs to be cooled before being used again, increasing the demands on the coolers and further reducing efficiency. In light of the foregoing, it can be seen that an oil system is needed that can provide oil in the quantity required according to a range of conditions being experienced by the engine.
Accordingly, there is a need for an improved lubrication schedule for a gas turbine engine.